This invention relates to drivers for inductive devices, and particularly to write drivers for inductive magnetic heads.
Inductive magnetic heads are commonly used in magnetic disk drives for writing data to magnetic disks. The magnetic head is operated by driving a write current through the inductive coil of the magnetic head, and reversing the direction of the current to reverse the magnetic field generated by the head. Field reversals induce changes in magnetic dipoles on the disk to represent data. While several types of current driver circuits are commonly used to drive current in opposite directions through the coil, one common circuit is an H-bridge. An H-bridge employs four transistor switches operated to direct write current through alternating pairs of the switches of the circuit. For optimal performance, the rise time of the write current at transitions should be as short as possible. Extended rise times adversely affect the field reversal characteristics and the recorded data. Current overshoots are often avoided because current overshoots usually generate undesirable undershoot, thereby creating ringing and increasing the settling time of the write current. While current overshoot is not necessarily an undesirable phenomenon, as overshoot often leads to quicker rise times, the undershoot delays settling time of the steady state write current thereby prohibiting implementation of short write current pulses.
Various techniques have been employed to suppress ringing in write driver circuits. Many of these techniques degrade the write current. For example, shunt impedances placed in parallel to the head coil suppress ringing, at the cost of diverting write current through the shunt impedance, making the diverted current unavailable to perform a write function at the head.
As technology of magnetic disk drives advances, it becomes increasingly desirable to increase data recording frequency, to thereby increase data density on the disk. Increased data frequency requires shorter and more rapid rise times to the write current pulses with quicker settling to the steady state write current value and without ringing. The present invention is directed to a technique for minimizing the rise time of the write current pulse and to reduce settling time.